Quantifying the Role of Importation on Sustained Malaria Transmission in a Low-to-Moderate Burden Region of Southwest Uganda

BACKGROUND: Parasite importation remains a challenge to malaria elimination. The extent to which human travel contributes to sustained transmission in low-to-moderate burden areas is poorly understood. METHODS: We conducted a 14-month longitudinal cohort study in Southwest Uganda. A total of 1918 individuals from 400 households were followed bimonthly. Travel histories and household characteristics were collected through surveys. Symptomatic and asymptomatic Plasmodium falciparum infections were captured through health facility surveillance and household reports (for symptomatic cases) and qPCR (for asymptomatic infections). Multilevel logistic regression models estimated associations between travel and infection. Population attributable fractions quantified travel's contribution to malaria. RESULTS: Over the study, 283 infections (244 symptomatic episodes and 39 asymptomatic infections) were recorded. Associations between travel and malaria varied spatially and temporally, with positive associations in lower transmission villages (OR = 4.38, 95% CI 1.80-10.64) and during periods of low transmission. Associations were strongest for short-distance trips to nearby areas of higher incidence. Population attributable fraction analyses suggested travel accounted directly for 14% of malaria cases in low-transmission villages overall, rising to 30% during periods of low transmission. CONCLUSIONS: Overnight travel contributed to malaria burden, particularly in low-transmission villages and during low seasons, highlighting the need for strategies that address both local transmission and importation.